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Thursday, September 9, 2010

Was everything I leaned in school wrong? Rethinking Fat

As many of you may know, my formal education was in nutrition not Exercise Science. As a student, I learned the conventional nutrition “wisdom” that was never to be questioned. One of the most strongly protected pieces of nutritional wisdom is that saturated fat is bad for you and will clog your arteries. But is this really true?

Almost every RD, MD, and Ph.D. believes it. Right? Not necessarily.

The role of saturated fats and heart disease is a hot button topic in nutrition today. This doesn’t filter down to the mainstream media, but many of the top minds in nutrition are re-examining this issue.

Just this month in the June edition of The American Journal of Clinical Nutrition there is an editorial entitled “Are refined carbohydrates worse than saturated fat?” The editorial written by Dr. Frank Hu, a medical doctor and professor of nutrition at the Harvard School of Public Health, contends that:

…diets that are typically low in fat (particularly saturated fat) and high in complex carbohydrates led to substantial decline in the percentage of energy intake from total and saturated fats in the United States. At the same time, it has spurred a compensatory increase in consumption of refined carbohydrates and added sugars-a dietary shift that may be contributing to the current twin epidemics of obesity and diabetes.

The changed landscape in obesity and dietary patterns suggests a need to reassess the dominant diet-heart paradigm and related dietary recommendations, i.e., the strategy of replacing total and saturated fats with carbohydrates.

This editorial references a study published in the May 2009 edition of the same journal that pooled the results from 11 American and European studies. In the study,replacing saturated fat calories with high GI carbohydrates actually increased the risk of heart disease!

Let’s look at one of the older studies often cited to support this hypothesis: The Seven Countries Study. Ancel Keys, a professor at the University of Minnesota, compared fat consumption in various populations with heart disease. The results were a nice and neat looking line graph. The data looked very convincing, but there was one huge problem. The databases Professor Keys used to plot the graph for the seven countries study contained data for 22 countries. When data for all 22 countries are plotted there is no correlation whatsoever between fat intake and heart disease.

The Framingham Heart Study is also frequently referenced, even though the data from this study shows no correlation between diet and serum LDL, HDL, or total cholesterol.

Yet Dr. William Kannel, the original director of the study, stated in a “clarification” of the results that even though there was no relationship between diet and serum cholesterol intake in the Framingham Study group, “it is incorrect to interpret this finding to mean that diet has no connection to blood cholesterol.”

Huh? The study found no connection between diet and serum cholesterol so how else can we interpret it?

Dr. William Castelli (Dr. Kannel’s successor as the head of the Framingham study) interpreted the data as “disappointing.” Here is his full quote, published in an article published in the Archives of Internal Medicine:

Most of what we know about the effects of diet factors, particularly the saturation of fat and cholesterol, on serum lipid parameters derives from metabolic ward-type studies. Alas, such findings, within a cohort studied over time have been disappointing; indeed the findings have been contradictory. For example, in Framingham, Mass, the more saturated fat one ate, the more cholesterol one ate, the more calories one ate, the lower the person’s serum cholesterol.

But even in ward-type studies that show an increase in bad cholesterol (LDL’s), there is also a proportional increase in good cholesterol (HDL’s). In addition, triglycerides are often lowered. Both high HDL’s and low triglycerides have been individually associated with reduced risk of cardiovascular disease. Any negative health impact from increased LDL’s is offset by this corresponding increase in HDL’s and decrease in triglycerides.

This would explain why in large population studies, a link between saturated fat intake and cardiovascular disease has never been shown. In both the Women’s Health Initiative (WHI) and the Multiple Risk Factor Intervention Trial (MR-FIT) no significant correlation was found between dietary consumption of saturated fat and cardiovascular disease! In both of these studies researchers admitted to being “disappointed” by the lack of results.

At first glance some studies will seem to support the ”saturated fat clogs arteries” hypothesis. For example, in one follow up analysis of the data from the Seven Countries Study researchers concluded in the abstract that “…saturated fat, vitamin C, and smoking are important determinants of all cause mortality.” But if you read thru the entire text you will see that the data showed no link between saturated fat consumption alone and age adjusted mortality. Only by grouping all three risk factors together (saturated fat, vitamin C, and smoking) were the researchers able to show a significant correlation.

“In controlled, long term studies saturated fat intake has never been linked to increases in cardiovascular disease or all cause mortality”

So what does this mean? Personally, I intend to stop worrying only about saturated fat and cholesterol. Other dietary factors, such as eliminating trans fats and other industrial seed oils, will have a much greater effect than reducing your intake of saturated fat and cholesterol.

- John Kuzora, originally published June 2010

1 comment:

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